Deoxygenation and reoxygenation kinetics of human red blood cells (rbc) suspended in a form of monolayer have been determined. Monolayer of rbc which interacts directly with the environmental gases is considered to mimic physiological gas-exchange observed in tissue capillaries. The results indicate that the kinetic gas-exchange of rbc not only depends upon the intracellular chemical constituents, but also the overall structure of rbc and the properties of the membranes. Effects of toxic gases and membrane reactants on these kinetic constants are now being investigated.